FVB.Cg-Smn1^tm1Hung Tg(SMN2)2Hung/J

Stock number: 005058
Product name: SMA-like
Strain synonyms: SMA-like mice line 2
Research areas: Neurobiology Research

Description

These mice exhibit a molecular and progressive neurodegenerative phenotype similar to Type III spinal muscular atrophy.

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Detailed description

Mice that are homozygous for the Smn1^tm1Hung knock-out allele and homozygous for the Tg(SMN2)2Hung transgene display a varied Type III SMA phenotype - they are viable, fertile and exhibit short and thickened tails. RT-PCR analysis detects alternative splicing of the transgene. Histological examination of tail tissue reveals atrophic muscles and subcutaneous edema. Skeletal muscle tissue has fewer myocytes and atrophic muscle bundles. Large motor neurons in the anterior horns of the spinal cord degenerate and are lost. There is a strong correlation between estimated copy number of the transgene and severity of the neurodegenerative phenotype. Of note, mice hemizygous for Tg(SMN2)2Hung have ~2 copies of the transgene, whereas mice homozygous for Tg(SMN2)2Hung have ~4 copies of the transgene.

Mice homozygous for Smn1^tm1Hung and hemizygous for Tg(SMN2)2Hung display a Type I SMA-like phenotype and die at ~14 days of age.

Mice that are heterozygous for Smn1^tm1Hung and hemizygous for Tg(SMN2)2Hung are phenotypically normal.

Non-transgenic (noncarrier) mice are phenotypically normal when heterozygous for Smn1^tm1Hung, but embryonic lethal when homozygous for Smn1^tm1Hung - failing to survive past embryonic day 6.5.

Importation of this model was supported by the Spinal Muscular Atrophy Foundation.

Development

Double mutant mice were generated by crossing transgenic mice carrying the human SMN2 gene with mice heterozygous for the Smn^tm1Hung targeted mutation.

The targeted mutant allele was generated by disrupting exon 7 with a vector containing neomycin resistance and herpes simplex virus thymidine kinase genes. This construct was electroporated into 129P2/OlaHsd-derived E14TG2a embryonic stem cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts and chimeric animals obtained. Chimeric animals were crossed to C57BL/6 for more than 5 generations.

The transgene consists of 115 kb of sequence from the SMN BAC clone 7C, including the entire human SMN2 coding region and flanking sequence. The transgenic construct was microinjected into male pronuclei of FVB/N mice. Founder line 2 (hemizygotes) were determined to have ~2 copies of the transgene. Founder line 2 was crossed to mice heterozygous for the targeted mutation, Smn^tm1Hung. The double mutant was then backcrossed to FVB/N for five generations.

Allele

Symbol: Tg(SMN2)2Hung
Name: transgene insertion 2, Hung Li
MGI accession ID: MGI:3056903
Generation method: Transgenic
Attributes: Inserted expressed sequence; Humanized sequence
Marker symbol: Tg(SMN2)2Hung
Marker name: transgene insertion 2, Hung Li
Chromosome: 4
Strain of origin: FVB/N
Expressed genes: SMN2,survival of motor neuron 2, centromeric,human
Molecular note: The transgene consists of 115kb of sequence from the SMN BAC clone 7C, including the entire human SMN2 coding region and flanking sequence. Five lines were generated.
General note: Five lines were generated.

Hemizygous transgenic mice that are also homozygous for Smn1^tm1Hung display:

• a range of spinal muscular atrophy (SMA)-like pathologies characterized as type 1, type 2, and type 3
  • Type 1 animals do not develop hairy fur, and die before postnatal day 10
  • Type 2 animals exhibit poor activity and variable symptoms, and die at approximately 2-4 weeks
  • Type 3 animals survive to adulthood and are fertile, but have short enlarged tails

• Transgene copy number correlates with the amount of protein that contains the region encoded by exon 7 and the severity of SMA-like phenotypes in these animals

Allele

Symbol: Smn1^tm1Hung
Name: targeted mutation 1, Hung Li
MGI accession ID: MGI:2383990
Generation method: Targeted
Attributes: Null/Knockout
Marker symbol: Smn1
Marker name: survival motor neuron 1
Chromosome: 13
Strain of origin: 129P2/OlaHsd
Molecular note: Exon 7 was replaced with an HPRT cassette via homologous recombination. Homozygous embryos were detected at E3.5 but not after E6.5.
General note: Homozygous mutant mice died during the peri-implantation stage.

In contrast, homozygous mutant mice carrying Tg(SMN2)1Hung display pathological changes in the spinal cord and skeletal muscles similar to those of patients with proximal spinal muscular atrophy (SMA). Some of these mice do not develop hairy fur, and die before postnatal day 10. Others exhibit poor activity and variable symptoms, and die at approximately 2-4 weeks. A third group of these mice survive to adulthood and are fertile, but have short enlarged tails. The variable severity of the pathological changes in these mice correlates with transgene copy number and the amount of protein that contains the region encoded by exon 7.